2nd batch of fixes for Soundcloud connector 

Follow-up to https://github.com/david-sabata/Chrome-Last.fm-Scrobbler/pull/367

Issues that needed attention:
- Better method to prevent double attachment with `window._ATTACHED`.
- Fix playback control interference (don't use `.off()` method).

Files are linted (with [Javascript Beautify](https://github.com/enginespot/js-beautify-sublime)) which causes a lot of changes.